Help with rewriting an URL with an .htaccess

Question

I need a .htaccess that will show this URL:

http://www.mysite.com/es/wp-content/plugins/mailpress/mp-includes/action.php?action=mail_link&add=123&lang=es

but will in fact serve this URL:

http://www.mysite.com/wp-content/plugins/mailpress/mp-includes/action.php?action=mail_link&add=123&lang=es

Note that action.php can receive other GET parameters in the URL. The htaccess must be able to foward them too. The only difference between these 2 URL is the "fake" root directory which will reflect the "lang" GET parameter.

Is it possible to do such things with a .htaccess (I'm pretty sure it's possible)? Anyone have pointers on how to do this??

Thanks!

Edit1: I forgot to say that the rewrite rule should be only valid for "action.php" that is in "/wp-content/plugins/mailpress/mp-includes/".

Edit2: I have this currently in my .htaccess:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Answer 1

The following should do the trick

RewriteEngine On
RewriteRule ^/es/(.+)$ /$1

With regard to the edit of your question, here's a modified answer:

RewriteEngine On
RewriteCond %{REQUEST_URI} ^/es/wp-content/plugins/mailpress/mp-includes/action.php
RewriteRule ^/es/(.+)$ /$1

Answer 2

try this one:

RewriteEngine on
RewriteRule ^/es/(.*) /$1

here is the according documentation from apache.